Method of making silicon iron compounds



Patented Aug. 18, 1931 UNITED STATES PATENT OFFICE JAMES A. PARSONS, orDAYTON, onro, ASSIGNOR TO THE DURIRON COMPANY, me, A

CORPORATION or new YORK METHOD OF MAKING SILII ICON IRON COMPOUNDS NoDrawing.

The invention relates to a method of making silicon iron compoundshaving definite desirable proportions of silicon and iron. The processis applicable in the making of ferrosilicon used in steel manufacture,to the making of acid resisting alloys, and to the making of othercompounds of steel and silicon where it is important that theproportions of silicon to steel or iron shall be accurately fixed. Theprocess has been developed for use particularly in connection with themaking of acid resisting iron in which the amount of silicon in thealloy must be held within relatively narrow limits in order to produce aroduct which is commercially satisfactory. n this alloy, the siliconshould range between 14.25% to 14.50%, since the product is too brittleif the silicon runs above the upper limit specified and lacks in acidresisting qualities if the silicon drops below the lower limit.Heretofore, these limits have been diflicult to attain, due to the factthat some silicon is lost during the melt, and to the fact that theferrosilicon which is used to provide the silicon does not run uniformas to its silicon content. As a result, it has been the practice tofirst melt up a quantity of ferrosilicon, analyze a sample, so that itsexact silicon content is known, and then use the ferrosilicon thusproduced in the melt from which the final alloy is made.

The method hereinafter described and claimed, avoids this difficulty andproduces a.-

product, without any preliminary melt, which is very close in itscontent of silicon to any redetermined content which may be selected.

In carrying out the process, the first part of the melt is accomplishedin the usual way, preferably in an electric furnace. Steel or iron andferrosilicon are mixed and melted with the proportions roughly adjustedso that the calculated amount of silicon is on the high side of theexact percentage desired; for instance, one or two per cent of siliconover a desired final content of 14.25%. As soon as the batch is melted,which occurs when the temperature is from 2450 degrees F. to 2550degrees F., a sample is removed in a test spoon or ladle and cast in achilled Application filed January 23, 1930. Serial No. 422,952.

metal mold to provide a bar one half inch in diameter and six incheslong. The use ofa mold of the kind specified is desirable in order togive a test bar of exact dimensions.

The test bar, as thus provided, is now tested for electrical resistance,this being done with any suitable testing apparatus, such as a standardKelvin bridge. This resistance, as thus determined, will indicate veryaccurately the amount of silicon in the melt. This has been found byrunning a large number of tests with a wide range of silicon contentsand establishing a graph or resistivity curve which is relatively smoothand uniform. By reference to this curve or to a table covering theresults of the determinations, the amount of silicon can be found bynoting the resistance in the test bar. To illustrate, a resistance inthe bar specified of 20 micro-ohms per cubic inch of alloy means asilicon content of 14.25% silicon; a resistance of 25'micro-ohms means asilicon content of 14.70% silicon; a resistance of 30 micro-ohms means asilicon content of 15%, etc. This electrical resistance determination ofthe silicon, .if properly done will not vary over one-tenth of one percent plus or minus from that found upon chemical analyses of the alloy.The most useful portion of the graph is that portion which indicates theresistance from about 14.25% of silicon upwards, as below such point thegraph curves in the reverse direction.

The determination of the silicon content can thus be accurately found infifteen min utes or less, and during the period in which the melt isattaining its proper pouring temperature of 2800 to 2900 degrees F.Assuming that the silicon content is on the high side of that desired inthe final alloy, this content is now reduced by adding to the melt anamount of iron suflicient (by calculation) to lower the silicon contentto exactly the per cent desired. It is desirable to proceed in this way,rather than to work on the low side of the silicon content, and then addsilicon to bring the alloy to the desired proportions, as the additionof silicon causes boiling in the melt tending to make the resultingcasting porous.

The whole operation can thus be carried out without loss of time,starting with ferro silicon in which the average silicon content is onlyroughl known, and a resulting alloy can be secure whose content ofsilicon is within one-tenth of one per cent plus or minus of anypredetermined content, which it is desired to produce. I have found thatthe carbon in the melt does not affect its resistivity where such carbonruns from 75 per cent of saturation to saturation and that therelatively small manganese content normally found in silicon steelalloys also does not affect their resistivity. It will be understoodthat the term iron is used in its generic sense to comprehend, inaddition to ordinary iron, the various grades of steel containing moreor less t'otal carbon.

In the making of commercial ferrosilicon, the raw materials are placedaround the electrodes in an electric furnace and fused in the usual Way,the materials ordinarily consisting of quartz, iron turnings, anthracitecoal, charcoal and coke, the constituents and their proportionsdepending on requirements and conditions. The silicon content hasheretofore been roughly determined by examining the fracture from asample and such content is of course not constant due to variations inthe materials and to other causes. The present procedure is equallyapplicable here, as samples of the product can be taken from time totime, their silicon content accurately determined electrically asheretofore explained, and the necessary additions or changes made in thematerials in order to give the desired silicon content. In this mannerthe silicon content can be kept much closer to the desired figure thanhas heretofore been possible.

What I claim is:

1. A method of making silicon iron compounds of substantially exactpredetermined proportions in which the silicon is above 14.25% whichconsists in fusing together as constituents ferrosilicon and iron in theapproximate calculated quantities necessary to give said predeterminedproportions, taking a sample from the melt before it has reached pouringtemperature, casting it into a test bar, and determining the proportionof silicon in the sample by measuring its electrical resistance duringthe period in which the temperature of the melt is being raised topouring temperature and then adding to the melt a quantity of one ofsaid constituents suflicient to bring the alloy to said predeterminedproportions.

2. A method of making silicon iron compounds of substantially exactpredetermined proportions in which the silicon content lies between14.25% and 18% which consists in fusing together ferrosilicon and ironin the JAMES A. PARSONS.

